Students Alternative Conceptions in Understanding of Sound

1
Students Alternative Conceptions in Understanding
of Sound

• Zdeslav Hrepic
• Kansas State University
• Physics Education Research Group

2
The Aim of Research and Methods

• The aim - to find or confirm
• students alternative conceptions related to the
  sound, their origins and representation
• Through written, open-ended, conceptual
  questions (in Croatian)
• During 1997, immediately after lectures on sound
• 287 examinees (divided in 4 groups - percentages)
• 3 levels - 8th grade elementary (El), high school
  (HS) and college level (Col)
• All in Split, Croatia

3
Sound Propagates As aParticle-Like Object (1of 2)

• The particles of the sound
• In water we hear sound from air weakly and
  unrecognizably because the particles of the sound
  can not penetrate the water. It has dense
  molecular structure (El)
• Sound breaks its way through materials
• "Sound propagates in the way that it acts with
  force on particles of material which it passes
  through. Denser the material sound propagates
  weaker..(El)

4
Sound Propagates As a Particle-Like Object (2
of 2)

• The sound occupies certain volume
• Sound passes slower in denser materials
  because it is dense and there is no space for it
  (El)
• Aerodynamics of sound
• ..sound of violin is thinner and faster in the
  air than sound of contrabass (El)
• Travels faster. Because violin sound is sharper
  (El)

5
Material Obstacles Slow Down Propagation of Sound
(60 - 19)

• the sound propagates slower if it comes across
  the barriers. (El)
• wooden barrier slows down speed of sound.(Col)

6
If Louder, Sound Travels Faster (36 - 60)

• Sound of stronger loudspeaker travels faster
  because it is stronger. (HS)
• Sound of stronger loudspeaker travels faster
  than sound of the weaker one. It travels faster
  because it has stronger power and sound
  automatically spreads faster. (El)

7
Speed of Sound Depends on Movement of Sound
Source (62 - 23)

• Sound of siren travels faster toward the
  observer when automobile moves toward the
  observer (Col) 43

• Stated reasons why
• Frequency is higher
• Distance gets shorter
• Speed of automobile carries that sound

• Speed of sound towards listener is increased for
  the amount of the speed of automobile. (HS)

8
Sound Energy Is Not Generally Transformable (68
- 13)

• Sound can not be transformed in some way into
  light because
• they are two completely different phenomenon
  (El)
• sound is mechanical wave, and light is
  electromagnetic.(Col)

• the sound is something perceived with ear and
  the light is perceived visually. (HS)
• the sound can not reach speed the of light.
  (HS)
• such a transformation of energy is not possible
  (HS)
• light is transversal, and sound is longitudinal
  wave. (HS)

9
Denser the Medium, Sound Propagates Faster (45 -
36) (1of 2)

• When the material is denser then the sound
  spreads faster. An example The sound is faster
  in water than in air (HS)

• For sound (mechanical wave) the medium is
  necessary. If it is necessary that means that if
  the material is denser the speed of the sound is
  greater. (HS)
• When the density is greater the sound is faster
  because the particles are nearer so the activity
  among them is conveyed faster. (Col)

10
Denser the Medium, Sound Propagates Faster (45 -
36) (2 of 2)

• "If particles of medium are denser, sound will
  move slower because it must break through this
  density. (El)

• "Less the density, greater propagating
  velocity...it is logical that if wave collides
  with particles, propagating velocity will be
  smaller. (Col)
• "Honey does not conduct sound, because its
  density is big enough to prevent propagation of
  sound. (Col)

11
Not All the Materials Can Conduct the Sound (44
- 45)

• PLASTICS
• 31 DOES NOT
• 9 conducts poorly
• 45 DOES conduct

• HONEY
• 44 DOES NOT
• 15 conducts poorly
• 30 DOES conduct

• Why NOT?
• Too Dense 30
• Insulator 1
• No explanation 13

• Why NOT?
• Its Structure 5
• Too Dense 3
• Too Stiff 3
• Insulator 3
• No explanation 18

12
Speed of Sound Depends on Its Frequency (47 -
37)

• speed depends on frequency so the higher is
  the frequency, the greater is the speed. (Col)
  37
• v?/T?f . The sound of the violin travels
  faster. (HS)

• The sound of the violin travels faster because
  it is thinner it produces more vibrations per
  second. I would describe it as the lighter sound,
  because the sound of the contrabass is deep, it
  spreads across the air very hardly. (El)

13
Wind Influences the Frequency of Received Sound
(33 - 10)
f?
Wind direction
a)
b)

• Yes, it will. The frequency will be higher if
  the speed of the sound is greater and vice
  versa. (HS) 23
• v ?/T, f 1/T v ?f ? vf (Col)
• We will have a feeling that the source was
  displaced and according to Dopplers effect it
  influences the frequency. (Col)

14
Conclusion Percentages and Categorization of
Students Difficulties
50 - affirm alt. conceptions 59 - 47 -
48 32 - negate alt. conceptions 21 - 36 - 42

• 1. Students models of propagation of the sound
  and their consequences particle particle
  pulses wave
• 2. Relation of the sound to the other physical
  phenomena (waves, light, energy, electricity,
  pressure, force)
• 3. Misinterpretations of graphics, formulas,
  definitions and terms learned in school
• http//www.phys.ksu.edu/zhrepic/